Method for coating tablets



United States Patent Office 3,256,111 Patented June 14, 1966 3,256,111METHOD FOR COATING TABLETS Robert E. Singiser, Guruee, IlL, assignor toAbbott Laboratories, North Chicago, 111., a corporation of Illinois NoDrawing. Continuation of application Ser. No. 32,516, May 31, 1960. Thisapplication Dec. 4, 1964, Ser. No. 416,101

5 Claims. (Cl. 117-85) This is a continuation of application Serial No.32,516 filed on May 31,- 1960, now abandoned.

This invention relates to tablet coatings and to a method of obtaining apharmaceutically-elegent tablet. More particularly, this inventionrelates to the glosscoating 'or shining of a previously-coatedpharmaceutical tablet.

The tablet-coating art has recently become aware of the advantages ofemploying the air-coating method for applying coating solutions totablets. Among the many advantages is the elimination of the familiarcoating pans and drying ovens, not to overlook the time-saving element.An example of such a method for air-coating tablets is described in U.S.2,648,609. Another technique for applying a coating solution by theair-coating method is described in co-pending application Serial No.11,364, now US. Patent 3,112,220, of which applicant is a jointinventor.

It is well-recognized in the tablet-coating art that a coating shouldhave a glossy finish in order to have a pleasing appearance. When thepan-coating method is employed for coating, the finished tablets areshiny due to the bufiing action which is exerted onthe table-ts bytumbling in the pan. On the other hand, when an aircoating method isemployed, the tablets receive no buffing action and consequently thefinish on the tablet is dull and unattractive. This is true whether aplastic film-coating as described in US. 2,881,085, or a standard sugarcoating, is applied to the tablets. Further, whether the tablets arecoated with certain plastic films or a sugar coating, and Whether thecoating is applied in the pan or by the air coating method, thesecoatings may be sensitive to high temperatures and humidity uponstorage, and become tacky.

It is therefore an object of the present invention to provide gloss on aprecoated tablet by the air-type coating method. It is another object ofthis invention to provide a tablet coating which provides improvedhightemperature and moisture resistance. It is a further object of thisinvention to provide elegant pharmaceutical tablets with a gloss coatingwhich does not prolong the disintegration time of the tablet.

These and other objects are accomplished. by the method of applying aprotective coating to previouslycoated tablets comprising formulating afluid coating composition consisting essentially ofhydroxypropylmethylcellulose containing 5-15 by weight of2-hydroxypropoxyl groups and 2732% by weight of methoxyl groups and alow-boiling, non-aqueous solvent for said hydroxypropylmethylcellulose,and directing a mixture of warm air and said coating compositionupwardly through a bed of said tablets to cause fiuidization of saidtablets, for a period of at least minutes. The above method of applyingthe protective coating or gloss coating comprises the newer airapplication method wherein the bed of tablets is maintained in fluidizedform and the coating composition is introduced in the form of a spray.

Briefly stated, the method comprises the forming of a columnar bed oftablets to be coated wherein the bed is preferably greater in heightthan it is in the horizontal cross-sectional dimension. An air stream isdirected upwardly through a portion of this bed with sufficient force tomove the tablets in that portion upwardly, thus forming a fluidizedspout of tablets. The spout extends above the top of the bed with thetablets falling therefrom back onto the top of the bed. In the parts ofthe bed adjacent the spout, the tablets move downwardly. The cellulosecoating material is atomized and introduced into the upwardly movingstream of air. The atomized cellulose fluid is deposited on the tabletsin the upwardly moving spout with the deposited liquid being dried bythe air.

In the above definition of the process, reference is made to the use ofwarm air. The temperature of this air is preferably between 30 and C. toprovide for fast evaporation of the low-boiling solvent used in thecoating composition, The low-boiling non-aqueous solvent referred toabove is preferably a solvent or solvent mixture which has a boilingpoint below about 80 C., e.g. ethanol, methanol, methylene chloride,chloroform, benzene, ethyl acetate, and mixtures thereof. The coatingsolution should contain between 10 and 50 grams of thehydroxypropyhnethylcellulose per liter, amount of fluid coating solutionemployed should be between 0.1 and 0.5 liter per kilogram of tablets.

To better understand the method of the present in vention, reference ismade to the following example which is meant as an illustration only.

Typical gloss-coating s0luti0n.-To a mixture of equal parts of methylenechloride and ethanol is added 20 grams of hydroxypropylmethylcellulosewith agitation. After a clear solution is formed, additional methylenechloride/ethanol (1:1) is added to produce a total volume of one liter,and the mixture is thoroughly stirred.

Typical coated tablets.A batch of 3 kg. of vitamin tablets weighing anaverage of 0.603 gram is placed in the coating chamber of anair-suspension tablet-coating apparatus with a coating chamber diameterof 15 cm. Air of 60 C. is pressed into this chamber at 4.2-4.7 mfi/min.The air-nozzle has an orifice of 1.75 mm. diameter; the coatingcomposition is introduced into the upwardly moving stream of air througha nozzle of 0.7 mm. diameter whereby it is atomized and deposited on thetablets. The coating solution has the following composition:

, Grams Hydroxypropylmethylcellulose of '50 c.p.s. 40.0 Yellow D & CLake #5. 60.0 Titanium dioxide 40.0 Saccharin sodium 2.0 Ethyl vanillin8.0 Castor oil 2.5

Methylene chloride/ethanol 1:1, q.s. to 2 liters.

The coating operation is completed when all the coating suspension isexhausted, or within about 15 minutes.

A short drying cycle follows, to strip residual solvent from the coatingchamber. The tablets are now covered by a plastic, colored, hardfilm-coating but have a dull appearance objectionable to many consumers.

Gloss c0ating.-The -dull, coated tablets are, without removal from thecoating chamber of the above aircoater, coated with the clear typicalgloss-coating solution shown above. Air of 60 C. is introduced into thecoating chamber at about 4.5 mP/min. and after about 10 minutes thetablets are elegant, shiny and, due to their gloss, easier to swallowthan the dull precoated tablets. Appropriate digestion studies show thatthere is no measurable time difference between the distintegration timesof the dull-coated and of the shiny glosscoated tablets.

Substantially the same results are obtained when the solvent system inthe typical gloss-coating solution is replaced by chloroform/ethanol,benzene, ethyl acetate, or methanol. Also, by replacing the precoatingformula and the given above with other standard coating solutions orsuspensions, the same beneficial effect is obtained with thegloss-coating of the present invention.

It is particularly interesting and noteworthy that the gloss-coating ofthe present invention adheres to precoated tablets regardless of thecomponents in the precoating film; whether the initial film containshydroxypropylmethylcellulose as the main film-forming comon ent or as aminor component, or whether hydroxypropylmethylcellulose is totallyabsent in the initial fi-lm, the gloss-coating composition applied bythe present method forms a shiny, protective and non-peeling film overthe initial coating.

The hydroxypropylmethylcellulose usedinthe present process has, amongothers, the advantages of being soluble in organic solvents and inwater. The water-solubility is of importance for the rapiddisintegration of the tablet in the bodys digestive liquids, and thesolubility in organic liquids makes the formulation of a glosscoatingsolution very simple: the protective film dries rapidly onto thetablets, and the gloss-coating operation takes only a very short time.Further, due to the high solubility of the hydroxypropylmethylcellulosein the body fluids, rapid excretion from the patients body is achieved.

The gloss-coating film provides the tablets so finished with aprotective layer that improves the stability of the tablets againstmoisture and high temperatures, even though the gloss-coating film needsto be no thicker than about microns. The film so applied is non-brittleand completely transparent so that color identifications or otherinsignia pressed onto the tablet sunface are plainly visible. A furtheradvantage of the present process is its applicability in an apparatusthat is frequently used for the initial coating operation. However, careshould be taken that the initial coating is completely dried before thegloss coating of the present process is applied. It is thus possible touse the air-suspension method for coating pharmaceutical tablets withany desired film suspension or solution, and after the tablets are driedin the same coating chamber by the supply of dry warm air thefilm-coating composition of the present process can be applied withoutever requiring the removal of the tablets from the coating apparatus.The gloss coating so applied not only has esthetic value but also servesas a seal to protect the colored coating from deleterious storageconditions without measurably influencing the disintegration time of thetablet.

Others may practice the invention in any of the numerous ways which willbe suggested to one skilled in the art by the present disclosure. Allsuch practice of the invention is considered to be a part hereof,provided it falls within the scope of the appended claims.

I claim:

1. The method of applying a protective glossy coating to previouslycoated and dried tablets comprising the steps of (formulating a fluidcoating composition consisting essentially ofhydroxypropylmethylcellulose containing 5-15 by weight ofZ-hydroxypropoxyl groups and 27-32% by weight of methoxyl groups as thesole film-forming component, and a nonaqueous solvent for saidhydroxypropylmethylcellulose, said solvent having a boiling point belowabout 80 C.,

directing a stream of air of a temperature between 30 and 80 C. upwardlythrough a bed of said coated tablets to cause fluidization of saidtablets, and introducing said fluid coating composition into said streamo-r' warm air for a period of at least 10' minutes to form a protectivecoating.

2. The process of claim 1 wherein the coating solution contains between10 and grams of hydroxypropylmethylcellulose per liter of coatingsolution.

3. The process of claim 1 wherein said fluid coating composition isapplied in the amount of between 0.1 and 0.5 liter per kilogram oftablets.

4. The process of claim 1 wherein said warm air has a temperaturebetween 30 and C. when entering the bed of said coated tablets.

5. The process of claim 1 wherein said coating composition is applied tothe fluidized bed of tablets for a period between 10 and minutes.

References Cited by the Examiner UNITED STATES PATENTS 2,648,609 8/1953Wurster 99l66 2,816,062 12/1957 Doerr 167--82 2,887,440 5/1959 Greiminer167-82 2,986,475 5/1961 Mesnard et al. 117100 3,015,609 1/1962 Sanders117-12 3,043,747 7/1962 Long 1 106-197 3,112,220 11/1963 Heiser, et al11824 OTHER REFERENCES Wurster; Air-Suspension Technique of Coating DrugParticles, Journal of the American Pharmaceutical Association, vol. 48,No. 8 451-454.

WILLIAM D. MARTIN, Primary Examiner.

S. W. ROTHSTEIN, Assistant Examiner.

1. THE METHOD OF APPLYING A PROTECTIVE GLOSSY COATING TO PREVIOUSLYCOATED AND DRIED TABLETS COMPRISING THE STEPS OF FORMULATING A FLUIDCOATING COMPOSITION CONSISTING ESSENTIALLY OFHYDROXYPROPYLMETHYLCELLULOSE CONTAINING 5-15% BY WEIGHT O2-HYDROXYPROPOXYL GROUPS AND 27-32% BY WEIGHT OF METHOXYL GROUPS AS THESOLE FILM-FORMING COMPONENT, AND A NONAQUEOUS SOLVENT FOR SAIDHYDROXYPROPYLMETHYLCELLULOSE, SAID SOLVENT HAVING A BOILING POINT BELOWABOUT 80*C., DIRECTING A STREAM OF AIR OF A TEMPERATURE BETWEEN 30 AND80*C. UPWARDLY THROUGH A BED OF SAID COATED TABLETS TO CAUSEFLUIDIZATION OF SAID TABLETS, AND INTRODUCING SAID FLUID COATINGCOMPOSITION INTO SAID STREAM OF WARM AIR FOR A PERIOD OF AT LEAST 10MINUTES TO FORM A PROTECTIVE COATING.